1. Field of the Invention
The present invention relates to a device applicable to micro machines such as micro motors, micro sensors, and micro relays, or micro electromechanical components collectively called Micro Electro Mechanical Systems (MEMS), and more particularly to a drive device for moving a movable body through utilization of operation fluid.
2. Prior Art
In recent years, there have been developed micro motors, micro sensors, micro switches, etc. which have sizes of several millimeters to several tens of microns and which are fabricated through utilization of a technique for micro-machining of materials, such as a semiconductor fabrication technique, or by making use of piezoelectric material or a like material which can effect mutual conversion between electrical energy and mechanical energy. These elementary devices can be widely applied to, for example, ink-jet printer heads, micro valves, flow sensors, pressure sensors, recording heads, actuators for tracking servos, on-chip biochemical analyzers, micro reactors, high-frequency components, micro magnetic devices, micro relays, acceleration sensors, gyroscopes, drive devices, displays, and optical scanners (Nikkei Micro Device, July 2000, pp. 164-165)
In these micro machines, electrostatic force is often used as drive force. Further, various types of drive sources have been studied, such as a type which utilizes distortion deformation of a piezoelectric material caused through application of voltage thereto, a type which utilizes changes in shape of a shape memory alloy, and a type which utilizes changes in volume of liquid caused by phase change thereof induced by heating. However, in micro mechanisms, force generated by a drive source and drive stroke become extremely small, and therefore, in some applications a mechanical amplification mechanism such as a lever must be combined with a drive source.
However, when the size of such a mechanical amplification mechanism is reduced to that of a micro machine, wear or sticking, which does not raise any problem in the case of a machine of ordinary size, raises a big problem. Further, since a micro machine having an amplification mechanism (drive function) such as a lever inevitably requires formation of a three-dimensional structure having a depth (height), micro machining of such a micro machine requires a longer time, and assembly of micro components requires a greater number of steps. For this reasons, some micro machines involve the problem that they are not suitable for mass production.
In view of the foregoing, an object of the present invention is to provide a drive device which uses operation fluid, which maintains the features of micro machines such as small size and low power consumption, which does not include a mechanical amplification mechanism having intrinsic problems of wear and sticking, which facilitates mass production, and which hardly causes leakage of operation fluid under variation in atmospheric temperature.
In order to achieve the above-described object, the present invention provides a drive device, comprising: a channel (flow-passage) forming portion for forming a channel (a flow passage), the channel accommodating an incompressible operation fluid and a movable body made of a substance different from that of the operation fluid, and being substantially divided into two operation chambers by means of the movable body; a pair of pumps each including a pump chamber communicating with the corresponding operation chamber and being filled with the operation fluid, an actuator provided for the pump chamber, and a diaphragm deformed by the actuator, the operation fluid within the pump chamber being pressurized or depressurized through deformation of the diaphragm; an internal-pressure-buffering-chamber-forming portion for forming an internal-pressure buffering chamber which accommodates the operation fluid and a compressible fluid for pressure buffering; and a micro flow passage (a micro channel) for connecting the channel of the channel forming portion and the internal-pressure buffering chamber of the internal-pressure-buffering-chamber-forming portion, the micro flow passage exhibiting a high passage resistance against abrupt pressure change of the operation fluid within the channel, to thereby substantially prohibit passage of the operation fluid through the micro flow passage and exhibiting a low passage resistance against slow pressure change of the operation fluid within the channel, to thereby substantially permit passage of the operation fluid through the micro flow passage. The micro flow passage may connect the channel of the channel-forming portion and the internal-pressure buffering chamber of the internal-pressure-buffering-chamber-forming portion directly, or via another portion (e.g., a connection passage for connecting the channel and the pump chamber, or a pump chamber). Further, three or more pumps may be provided.
By virtue of the above-described configuration, when the diaphragm is deformed by the actuator, the operation fluid within the channel is pressurized or depressurized. At this time, when the pressure of the operation fluid changes abruptly, the micro flow passage exhibits a high passage resistance in order to substantially prohibit passage of the operation fluid through the micro flow passage. Therefore, the pressure change of the operation fluid is transmitted to the movable body within the channel, so that the movable body moves. In contrast, when the pressure of the operation fluid changes slowly due to thermal expansion of the operation fluid caused by variation in the ambient temperature or due to slow operation of the actuator, the micro flow passage exhibits a low passage resistance in order to substantially permit passage of the operation fluid through the micro flow passage. Therefore, the operation fluid moves via the micro flow passage to the internal-pressure buffering chamber, which accommodates a compressible fluid for pressure buffering. As a result, pressure increase of the operation fluid within the channel is suppressed, and it becomes possible to avoid breakage of the device due to excessive pressure of the operation fluid and to prevent leakage of the operation fluid due to breakage of the device.
Preferably, the actuator includes a film-type piezoelectric element consisting of a piezoelectric/electrostrictive film or an antiferroelectric film and electrodes; and the diaphragm is formed of ceramic.
In this case, micro machining can be performed more easily, and drive devices which are well suited for mass production and which have excellent durability can be provided.
Moreover, with the drive device it is preferred that each of the diaphragms of the pump should form part of the wall of each of the pump chambers and should be disposed such that it has the membrane surface on the same plane, that the channel of the channel forming portion should be configured such that it constitutes a space having its longitudinal direction within a plane parallel to the membrane surface of the diaphragm, that the micro flow passage of the micro flow passage portion should be extended in a direction parallel to the membrane surface of the diaphragm and that the internal pressure buffering chamber of the internal-pressure-buffering-chamber-forming portion should be configured such that it constitutes a space having its longitudinal direction within a plane parallel to the membrane surface of the diaphragm and should be disposed such that it communicates with the channel of the channel forming portion via the micro flow passage of the micro flow passage portion.
When each of the pump chambers is configured, for example, such that a diaphragm, made of a single plate such as deformable ceramic sheet, forms part of the wall of the pump chamber, the actuation of each of the actuators allows the volume of each pump chamber to be directly changed, thus allowing efficient pressurization or depressurization of the operation fluid. Therefore, it is appropriate that each of the diaphragms of the pump should be disposed such that it forms part of the wall of each of the pump chambers and has the membrane surface within the same plane.
On the other hand, while the cross-section of the micro flow passage needs to be small in order to provide a flow passage resistance (a channel resistance) having the characteristics, an excessively small cross-section requires machining accuracy, resulting in higher device manufacturing costs. In connection with this, it is possible for the micro flow passage to provide a flow passage resistance having the characteristics by securing the length of the channel (lengthening the channel). However, if the micro flow passage is extended only in a direction in which the path interests with the diaphragm""s membrane surface (for example, a direction to allow intersection with the diaphragm""s membrane surface at a right angle), the drive device needs to be thick.
Therefore, if the micro flow passage of the micro flow passage portion is configured as described in the configuration such that the channel is extended in a direction parallel to the diaphragm""s membrane surface and such that the channel of the channel forming portion and the internal pressure buffering chamber of the internal-pressure-buffering-chamber-forming portion, each of which is a space having its longitudinal direction within a plane parallel to the membrane surface of the diaphragm, are disposed and configured to allow communication with each other via the micro flow passage, it is possible to dispose the channel, the internal pressure buffering chamber and the micro flow passage within the thickness of each of them. Thus, very thin (slim) drive devices can be provided. Moreover, since it is possible to increase the surface area of such a slim drive device relative to the overall volume of the device, heat generated by operation can be readily radiated externally, thus ensuring stable operation.